High 7.5Published Sep 26, 2026

CVE-2026-100664Netty 4.2.2 through 4.2.17 HTTP/1 Host Header Authority Confusion

Updated under an hour ago (2026-10-19 05:50 UTC)

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EPSS puts the chance of exploitation in the next 30 days at 0.33%, higher than 24% of scored CVEs.

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Exploited in the last 30 days

Netty's HTTP/3 codec (io.netty:netty-codec-http3) versions 4.2.2.Final through 4.2.17.Final builds the HTTP/3 :authority pseudo-header from the HTTP/1 Host header before considering the authority of an absolute-form HTTP/1 request-target. In HttpConversionUtil.toHttp3Headers(HttpMessage, boolean) — reached via Http3FrameToHttpObjectCodec(false) — a non-empty Host header takes precedence over the request-target authority, contrary to the HTTP/1.1 rule that a server receiving an absolute-form request-target must ignore the Host header. In a Netty-based HTTP/1-to-HTTP/3 gateway, proxy, or protocol bridge, a remote client can send a request such as "GET https://trusted.example/admin HTTP/1.1" with "Host: attacker.example", causing components that validate, authorize, or route on the RFC-defined request-target authority to reach a different decision than the upstream HTTP/3 peer, which receives :authority derived from the conflicting Host header. This authority confusion can affect virtual-host routing, allow-list checks, backend selection, cache keys, and URL generation. The advisory reports integrity impact only (no code execution, memory corruption, or availability impact). Fixed in 4.2.18.Final.

CVSS: 7.5 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Weakness (CWE): CWE-20
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): 0.33% (percentile 24)
Assigned by: VulnCheck
NVD analysis: Deferred
Record last updated: Sep 28, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

netty netty netty:netty (from the name)	from 4.2.2.Final before 4.2.18.Final; 4.2.18.Final not affected	CNA record

References

https://github.com/netty/netty/security/advisories/GHSA-hfr2-x62w-v49hvendor-advisory
https://www.vulncheck.com/advisories/netty-4.2.2-through-4.2.15-http-1-host-header-authority-confusionthird-party-advisory

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.